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Category:   Application (Generic)  >   BIND Vendors:   ISC (Internet Software Consortium)
(FreeBSD Issues Fix) BIND DNS Query Port Entropy Weakness Lets Remote Users Spoof the System
SecurityTracker Alert ID:  1020474
SecurityTracker URL:  http://securitytracker.com/id/1020474
CVE Reference:   CVE-2008-1447   (Links to External Site)
Date:  Jul 14 2008
Impact:   Modification of system information
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 9.x
Description:   A vulnerability was reported in BIND. A remote user can spoof the system.

The domain name system (DNS) service does not use sufficiently random UDP sockets to process queries. A remote user can send specially crafted DNS queries and responses to the target service to spoof responses and insert records into the DNS cache. This may cause traffic to be redirected to arbitrary IP addresses specified by the remote user.

The vendor indicates that the vulnerability exists in the DNS protocol itself, rather than in any particular vendor's implementation.

Systems using BIND as a caching resolver are affected.

Some demonstration exploit code is available at:

http://www.caughq.org/exploits/CAU-EX-2008-0002.txt
http://www.caughq.org/exploits/CAU-EX-2008-0003.txt

Dan Kaminsky of IOActive reported this vulnerability.
Impact:   A remote user can spoof the DNS service, causing traffic to be redirected to arbitrary hosts.
Solution:   FreeBSD has released a fix and has provided the following solution instructions [quoted]:

The following patches have been verified to apply to FreeBSD 6.3 and
7.0 systems.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

[FreeBSD 6.3]
# fetch http://security.FreeBSD.org/patches/SA-08:06/bind63.patch
# fetch http://security.FreeBSD.org/patches/SA-08:06/bind63.patch.asc

[FreeBSD 7.0]
# fetch http://security.FreeBSD.org/patches/SA-08:06/bind7.patch
# fetch http://security.FreeBSD.org/patches/SA-08:06/bind7.patch.asc

b) Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch
# cd /usr/src/lib/bind
# make obj && make depend && make && make install
# cd /usr/src/usr.sbin/named
# make obj && make depend && make && make install

NOTE WELL: This update causes BIND to choose a new, random UDP port for
each new query; this may cause problems for some network configurations,
particularly if firewall(s) block incoming UDP packets on particular
ports. The avoid-v4-udp-ports and avoid-v6-udp-ports options should be
used to avoid selecting random port numbers within a blocked range.

NOTE WELL: If a port number is specified via the query-source or
query-source-v6 options to BIND, randomized port selection will not be
used. Consequently it is strongly recommended that these options not
be used to specify fixed port numbers.

The FreeBSD advisory is available at:

http://security.FreeBSD.org/advisories/FreeBSD-SA-08:06.bind.asc
Vendor URL:  www.isc.org/index.pl?/sw/bind/index.php (Links to External Site)
Cause:   Randomization error
Underlying OS:   UNIX (FreeBSD)

Message History:   This archive entry is a follow-up to the message listed below.
Jul 8 2008 BIND DNS Query Port Entropy Weakness Lets Remote Users Spoof the System


 Source Message Contents
Date:  Sun, 13 Jul 2008 19:10:05 +0000 (GMT)
Subject:  FreeBSD Security Advisory FreeBSD-SA-08:06.bind


-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

=============================================================================
FreeBSD-SA-08:06.bind                                       Security Advisory
                                                          The FreeBSD Project

Topic:          DNS cache poisoning

Category:       contrib
Module:         bind
Announced:      2008-07-13
Credits:        Dan Kaminsky
Affects:        All supported FreeBSD versions.
Corrected:      2008-07-12 10:07:33 UTC (RELENG_6, 6.3-STABLE)
                2008-07-13 18:42:38 UTC (RELENG_6_3, 6.3-RELEASE-p3)
                2008-07-13 18:42:38 UTC (RELENG_7, 7.0-STABLE)
                2008-07-13 18:42:38 UTC (RELENG_7_0, 7.0-RELEASE-p3)
CVE Name:       CVE-2008-1447

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:http://security.FreeBSD.org/>.

I.   Background

BIND 9 is an implementation of the Domain Name System (DNS) protocols.
The named(8) daemon is an Internet Domain Name Server.  DNS requests
contain a query id which is used to match a DNS request with the response
and to make it harder for anybody but the DNS server which received the
request to send a valid response.

II.  Problem Description

The BIND DNS implementation does not randomize the UDP source port when 
doing remote queries, and the query id alone does not provide adequate
randomization.

III. Impact

The lack of source port randomization reduces the amount of data the
attacker needs to guess in order to successfully execute a DNS cache
poisoning attack.  This allows the attacker to influence or control
the results of DNS queries being returned to users from target systems.

IV.  Workaround

Limiting the group of machines that can do recursive queries on the DNS
server will make it more difficult, but not impossible, for this
vulnerability to be exploited.

To limit the machines able to perform recursive queries, add an ACL in
named.conf and limit recursion like the following:

acl example-acl {
   192.0.2.0/24;
};

options {
	recursion yes;
	allow-recursion { example-acl; };
};

V.   Solution

Perform one of the following:

1) Upgrade your vulnerable system to 6-STABLE or 7-STABLE, or to the
RELENG_7_0 or RELENG_6_3 security branch dated after the correction
date.

2) To patch your present system:

The following patches have been verified to apply to FreeBSD 6.3 and
7.0 systems.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

[FreeBSD 6.3]
# fetch http://security.FreeBSD.org/patches/SA-08:06/bind63.patch
# fetch http://security.FreeBSD.org/patches/SA-08:06/bind63.patch.asc

[FreeBSD 7.0]
# fetch http://security.FreeBSD.org/patches/SA-08:06/bind7.patch
# fetch http://security.FreeBSD.org/patches/SA-08:06/bind7.patch.asc

b) Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch
# cd /usr/src/lib/bind
# make obj && make depend && make && make install
# cd /usr/src/usr.sbin/named
# make obj && make depend && make && make install

NOTE WELL: This update causes BIND to choose a new, random UDP port for
each new query; this may cause problems for some network configurations,
particularly if firewall(s) block incoming UDP packets on particular
ports.  The avoid-v4-udp-ports and avoid-v6-udp-ports options should be
used to avoid selecting random port numbers within a blocked range.

NOTE WELL: If a port number is specified via the query-source or
query-source-v6 options to BIND, randomized port selection will not be
used.  Consequently it is strongly recommended that these options not
be used to specify fixed port numbers.

VI.  Correction details

The following list contains the revision numbers of each file that was
corrected in FreeBSD.

Branch                                                           Revision
  Path
- -------------------------------------------------------------------------
RELENG_6
  src/contrib/bind9/bin/named/client.c                        1.1.1.2.2.5
  src/contrib/bind9/bin/named/server.c                        1.1.1.2.2.4
  src/contrib/bind9/lib/dns/api                               1.1.1.2.2.5
  src/contrib/bind9/lib/dns/dispatch.c                        1.1.1.1.4.4
  src/contrib/bind9/lib/dns/include/dns/dispatch.h            1.1.1.1.4.3
  src/contrib/bind9/lib/dns/resolver.c                        1.1.1.2.2.8
RELENG_6_3
  src/UPDATING                                             1.416.2.37.2.8
  src/sys/conf/newvers.sh                                   1.69.2.15.2.7
  src/contrib/bind9/bin/named/client.c                    1.1.1.2.2.3.2.1
  src/contrib/bind9/bin/named/server.c                    1.1.1.2.2.2.2.1
  src/contrib/bind9/lib/dns/api                           1.1.1.2.2.3.2.1
  src/contrib/bind9/lib/dns/dispatch.c                    1.1.1.1.4.2.2.1
  src/contrib/bind9/lib/dns/include/dns/dispatch.h        1.1.1.1.4.1.2.1
  src/contrib/bind9/lib/dns/resolver.c                    1.1.1.2.2.6.2.1
RELENG_7
  src/contrib/bind9/bin/named/client.c                        1.1.1.6.2.2
  src/contrib/bind9/bin/named/server.c                        1.1.1.6.2.2
  src/contrib/bind9/lib/dns/api                               1.1.1.6.2.2
  src/contrib/bind9/lib/dns/dispatch.c                        1.1.1.4.2.2
  src/contrib/bind9/lib/dns/include/dns/dispatch.h            1.1.1.3.2.2
  src/contrib/bind9/lib/dns/resolver.c                        1.1.1.9.2.2
RELENG_7_0
  src/UPDATING                                              1.507.2.3.2.7
  src/sys/conf/newvers.sh                                    1.72.2.5.2.7
  src/contrib/bind9/bin/named/client.c                    1.1.1.6.2.1.2.1
  src/contrib/bind9/bin/named/server.c                    1.1.1.6.2.1.2.1
  src/contrib/bind9/lib/dns/api                           1.1.1.6.2.1.2.1
  src/contrib/bind9/lib/dns/dispatch.c                    1.1.1.4.2.1.2.1
  src/contrib/bind9/lib/dns/include/dns/dispatch.h        1.1.1.3.2.1.2.1
  src/contrib/bind9/lib/dns/resolver.c                    1.1.1.9.2.1.2.1
- -------------------------------------------------------------------------

VII. References

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-1447
http://www.kb.cert.org/vuls/id/800113

The latest revision of this advisory is available at
http://security.FreeBSD.org/advisories/FreeBSD-SA-08:06.bind.asc
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